Black-body radiation


by nag555
Tags: blackbody, radiation
nag555
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#1
Feb27-12, 07:14 AM
P: 5
why can't a black-hole absorb its own black body radiation? (Black body radiation is also and electro magnetic field like light and so a black-hole with its intense gravitational field is expected not to emit even blackbody radiation also!!!!)
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zhermes
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#2
Feb27-12, 08:47 AM
P: 1,262
Hi nag555, welcome to physicsforums!
A black-hole does absorb a lot of its own radiation; basically all of it that isn't directed exactly (radially) outward----but the radiation that is directed outward, is able to escape.
nag555
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#3
Feb27-12, 09:57 PM
P: 5
in that case, any person who jumps on earth radially outward should also escape gravity!!!!!

Nabeshin
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#4
Feb27-12, 10:34 PM
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Black-body radiation


Please read this to clarify:
http://en.wikipedia.org/wiki/Hawking_radiation
Drakkith
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#5
Feb27-12, 11:55 PM
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Quote Quote by nag555 View Post
why can't a black-hole absorb its own black body radiation? (Black body radiation is also and electro magnetic field like light and so a black-hole with its intense gravitational field is expected not to emit even blackbody radiation also!!!!)
Any radiation released inside the event horizon will not escape. Radiation released outside it by in-falling material can escape if it is emitted in the right direction. Hawking radiation is different and is not like black body radiation. See the link in the previous post for information on it.
zhermes
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#6
Feb28-12, 12:10 AM
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Quote Quote by nag555 View Post
in that case, any person who jumps on earth radially outward should also escape gravity!!!!!
Why? People can't jump as fast as light....

The closer to an event horizon an object is, the faster it needs to move (for our purposes, in the radial direction) to escape. As the object approaches the event horizon, the escape (radial) velocity approaches the speed of light.
nag555
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#7
Feb28-12, 12:39 AM
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thank you for your response....it is clear now..


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